<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 100px;
            height: 100px;
            background: red;
        }
    </style>
</head>
<body>
    <div class="box"></div>
    <script>
        var boxEle = document.querySelector(".box");
        var flag = true;
        document.onclick = function(){
            if(flag){
                boxEle.style.display = "none";
            }else{
                boxEle.style.display = "block";
            }
            flag = !flag;
            // console.log(flag);

            // 
        }



    </script>
</body>
</html>